1. Technical Field
The present disclosure relates to a technique for generating an image of a target object on a virtual focal plane on the basis of a plurality of images captured with a plurality of light sources in a lensless microscope.
2. Description of the Related Art
The demand that a cultured cell be observed continuously without staining the cell is present in many fields in which a cultured cell is used for a medical purpose or an industrial purpose, such as cell production for treatment or drug efficacy study. However, cells are largely colorless and transparent, and thus the three-dimensional structure of a cultured cell is hard to observe from an image captured with an optical microscope that uses transmitted light.
In order to evaluate a sectional shape of a cell, Japanese Unexamined Patent Application Publication No. 2013-101512 discloses a method of generating a focal image (pseudo-sectional image) of a plane that is not parallel to an objective lens from a number of images of a target object that are focused at different heights on the target object along a plane parallel to the objective lens (i.e., a number of images captured while moving the focus in the height-wise direction of the target object).
Continuous observation of a cultured cell is carried out within a restricted space as in an incubator for maintaining a high-humidity environment for culturing a cell. In order to carry out observation in such a high-humidity and restricted space, U.S. Patent Application Publication No. 2014/0133702 discloses a lensless microscope that makes it possible to observe a tiny cell without using a lens. A method of increasing the resolution by superimposing a plurality of images captured by illuminating a target object from a plurality of different positions (Ptychography) is disclosed.
However, according to the method disclosed in Japanese Unexamined Patent Application Publication No. 2013-101512, fragmentary images are cut out from the captured images focused at different height positions, and the cut-out fragmentary images are connected together. Thus, discontinuity appears at a portion where the fragmentary images are connected. As a result, the image quality of the pseudo-sectional image deteriorates due to the discontinuity. In addition, if blurring processing is carried out on the discontinuous portion in order to reduce the deterioration in the image quality associated with the discontinuity, the sharpness of the pseudo-sectional image decreases.